This invention relates to an internal overload clutch assembly which permits rotation between a rotating member and a rotatable member during normal operation, but which disconnects the rotating and rotatable members from each other when a maximum torque is exceeded.
In order to couple and uncouple drive shafts from driven shafts, a variety of styles of torque overload clutches or couplings have been developed. While prior art developments in torque overload clutches has been extensive, they can be generally described according to their construction and operation. Many of these clutch or coupling devices are in the category of flexible couplings which provide transmission of the driving, rotational, or torque force from a drive shaft to the intended driven shaft, but which are capable of disconnection when a binding force creates an excessive torque causing significantly reduced turning of a mechanical operator on a work component. In certain cases, the flexible couplings are provided with safety features which prevent excessive torque forces on the driven shaft from damaging the drive means and/or its prime mover. Many of the safety devices employed in flexible couplings include magnetically activated torque coupler devices as shown, for example, in U.S. Pat. No. 2,771,171. Another variety of magnetic coupling-clutch devices is shown in U.S. Pat. Nos. 3,221,389 and 3,339,819 which use mechanical elements that engage/disengage relative to one another, together with permanent magnets. Further types of magnetic torque limiting devices used in low force operating mechanisms, such as phonograph record players or sound recorders, are shown in U.S. Pat. Nos. 1,136,739 and 2,300,778. Other types of magnetic couplers include those which have spring biasing to determine the degree of force necessary for disengaging the coupling as shown in U.S. Pat. No. 3,053,365. Other forms of connectors which have utilized permanent magnet designs for effecting torque control are shown in U.S. Pat. Nos. 3,277,669, 3,159,725, 2,943,216 and 2,885,873; and those types of magnetic couplers which use a frictional connection between magnets to determine the degree of torque necessary to effect uncoupling of the torque limiting device as shown, for example, in U.S. Pat. No. 2,746,691.
In addition to magnetic coupler designs, various mechanical coupling devices, using ball and detent couplings for holding driving and driven parts together until separated by excessive torque are shown in U.S. Pat. Nos. 3,701,404, 3,680,673, 3,893,553, 3,981,382, 3,979,925, 3,942,238, 3,927,537, 3,930,382 and 3,866,728. Some mechanical coupling devices employ ball-bearing type means as the coupling/uncoupling element such as shown in U.S. Pat. Nos. 1,833,164, 3,722,644 and 3,774,738. Other types of power transmitting mechanisms having flexible couplings therein are shown in U.S. Pat. Nos. 1,541,489, 1,566,553, 2,818,712, 3,050,965, 3,148,499, 3,942,337, 4,006,608 and 4,046,237.
Along with the aforementioned categories, there is yet another category which has been developed by inventors employed by the assignee of the present invention. In U.S. Pat. Nos. 4,174,621 and 4,373,923, this particular type of mechanical torque limiting overload coupling/clutching device has been disclosed. In both of these patents, an improved overload torque coupler/clutch device has been developed in which suspended ball detents are used to interconnect rotating and rotatable members during normal operation, but upon encountering an excessive torque force on the rotatable member, suspended ball detents are shifted against a resilient spring out of seating engagement to disconnect the rotating and rotatable members. This improved style of torque limiting overload coupling minimizes rotational back lash or looseness, while maintaining precision operation of the rotatable member. In addition, a more precise and consistent de-coupling of the assembly is provided when a trip torque is encountered, and significant damage to the ball detents has been minimized. Such torque limiting overload coupling devices have been particularly useful in conjunction with cam indexing systems such as shown in U.S. Pat. No. 3,817,116, for example, which is also assigned to the same assignee of the present invention. The construction and operation of such cam operation systems include the use of radially mounted cam followers which are indexed by specifically designed multi-ribbed cams. The cam surfaces engage cam followers mounted on a hub to provide accurate positioning, while allowing clearance between adjacent cam followers. Mechanical torque limiting overload couplings which have been employed in conjunction with such cam indexing systems, have been operated as separate components, separate from, but operative with such systems. Thus, a typical set up would include a cam index system, with or without a separate speed reducer, and also a separately mounted torque limiting overload coupling which is mounted outside the housing of the cam index system, but which couples/uncouples the output driven shaft or flange thereof, to connect and disconnect the drive shaft or prime mover when an excessive torque is encountered.
In certain industries, however, it is necessary to expose all of the aforementioned mechanical components and driving systems to daily cleaning. In the dairy industry, for example, the incidence of salmonella poisoning or other contamination requires daily washing of operating machine components. This subjects the operating machine components to unnecessary exposure to moisture and deterioration, even though stainless steel may be used in the construction thereof. This has created a need for a self enclosed torque limiting clutch assembly which is contained in the same housing as the indexing system or prime mover. While it may appear at first sight that this would not require extensive engineering design and improvement in view of the highly developed nature of the prior art in this field, in actual fact; however, the development of the present invention did not come easily. Numerous designs were conceived and tested, some including magnetic coupler devices, but were unsuccessful. After much development and testing the internal overload clutch assembly of U.S. Pat. No. 4,828,095, which is also assigned to the same assignee of the present invention and which is incorporated herein by reference, was developed. The overload clutch assembly of that patent, however, was developed for use with a right angle indexer. There, however, is a need for an internal overload clutch assembly which can be used in parallel shaft indexers.